The present invention relates to low temperature sealing glass compositions using ceramic composite filler useful for sealing alumina ceramic package, in particular, to compositions for hermetic-sealing cap and base of alumina package which consists of a solid PbO-B.sub.2 O.sub.3 glass powder and a filler selected from zinc zirconium silicate composite or magnesium aluminum zirconium silicate composite as a low expansion ceramic composite.
Recently, semi-conductor is high-integrated because of large capacity, so IC chip capacity tends to be increased, but its size be decreased.
And, since the application field of alumina package has more severe ambient condition than that of the plastic package, the higher mechanical strength of the sealed package must be maintained in the small sealing area. Therefore, the sealing composition for the above field has to be satisfied with basic properties such as electrical properties, chemical durability and the like required for sealing of alumina package, and simultaneously to have high mechanical strength.
The known sealing glass compositions for sealing alumina ceramic packages consist of a vitreous PbO-B.sub.2 O.sub.3 glass powder and one or two low thermal expansion ceramic fillers such as .beta.-eucryptite, cordierite, willemite, zircon, and the like.
Since .beta.-eucryptite, cordierite, and willemite have the thermal expansion coefficient below 20.degree..times.10.sup.-7 /.degree.C., the sealing compositions using them as a single filler with a low temperature glass may have a suitable thermal expansion coefficient corresponding to alumina package and a suitable fluidity at the sealing temperature. However, a high sealing strength cannot be maintained due to low intrinsic mechanical strength of the filler and microcracks occurred by large difference in thermal expansion coefficient between the used filler and the vitreous glass powder. For example, in order to reduce the microcracks formed at the interface between the filler and the vitreous glass component, the particle size of filler must be small, but in this case, the fluidity of sealing composition is decreased and its acid durability is also decreased due to increased surface area. In order to solve these problems, there is an improved prior art in which the sealing glass composition of two filler system consists of one of above fillers and zircon or tin oxide solid solution. But, in this case, it is still required to improve the mechanical strength and acid durability for hermetic sealing of alumina package.
On the other hand, zircon has to be added in an excessive content to the sealing composition in comparison with willemite or cordierite due to its high thermal expansion coefficient(20.degree..about.40.degree..times.10.sup.-7 /.degree.C.) in order to correspond to the thermal expansion coefficient of alumina package. And zircon as disclosed on Japanese Patent Publication No. 4-28657 can not be synthesized densely without sintering additives such as Fe.sub.2 O.sub.3, ZnO, or MnO.sub.2. The above sintering additives are segregated in the grain boundary of the sintered zircon and cause to increase the thermal expansion coefficient and dielectric loss. And, in case willemite, a sintering product can be only by heat-treating over 24 hours at high temperature as U.S. Pat. No. 4,522,925. Finally, to obtain dense cordierite without sintering additives is very difficult because of its very narrow sintering temperature range.
As the result of the above, it is acutely required to easily synthesize a new filler having the thermal expansion coefficient in the range of 20.degree..about.40.degree..times.10.sup.-7 /.degree.C. and simultaneously having high mechanical strength and chemical durability.